Along with a constantly increasing data rate and service load as required, a conventional access over single-layer coverage by a macro base station has failed to satisfy the demand, and consequently existing systems have come to gradually attempt an access over layered coverage, that is, some low-power base stations, e.g., a Home eNodeB, a pico base station, a femto base station, a relay node, etc., are deployed in a hotspot area or indoors to cooperate with the macro base station for signal coverage to thereby well satisfy the constantly increasing demand. A low-power base station is a base station device used in a home indoor environment, an office environment or another hotspot low-coverage environment to enable an operator to offer a more appealing service at a higher data rate and a lower cost. Particularly the femto base station restricts an accessing member subscriber somehow while disallowing a non-member subscriber for an access, and if the non-member subscriber enters a coverage area of the femto base station, then the subscriber has to reside at an accessible base station (e.g., the macro base station) with use of an Almost Blank Subframe (ABS) based upon a TDM Inter-Cell Interference Coordination (ICIC) (an interference subframe obviation mechanism); otherwise, the subscriber may enter a coverage hole due to a strong signal of the femto base station and consequently become inoperative. If the pico base station is at the same frequency as the macro base station, then the subscriber also may become inoperative due to strong interference, and also the interference problem has to be addressed with use of an ABS subframe based upon the TDM ICIC mechanism.
For example, referring to FIG. 1, a UE1 is served by a macro base station, and a femto base station can only serve an authorized CSG (Closed Subscriber Group) subscriber, and since a UE2 is a CSG subscriber, the subscriber can access the femto base station after being authenticated, but when the UE1 is located in a coverage area of the femto base station, since the UE1 is a UE served by the macro base station (referred to as an MUE) instead of an authorized CSG subscriber, even if the strength of a signal of the femto base station is currently far above the strength of a signal of the macro base station, the UE1 can not be switched to the femto base station and may be further subjected to strong interference from the femto base station, and as such the subscriber UE1 may suffer from a very poor channel condition, a call drop and even inoperability. In the existing LTE protocol, the problem of downlink interference in the foregoing situation can be addressed in the following particular ABS subframe obviation solution:
Due to strong interference of the femto base station to the macro base station, ABS subframes can be used at the femto base station for avoidance, where at the network side, the macro base station and the femto base station coordinate allocation of the subframes between them and notify the UE of a coordination result, so when the non-member MUE becomes inoperative due to strong interference of the femto base station, an ABS subframe obviation configuration is applied so that the MUE measures and transmits data only in the ABS subframes notified of by the network side, particularly as illustrated in FIG. 2. Since the femto base station stops scheduling of data fields and transmits only CRS (Common Reference Signal) (common pilot) signals in the ABS subframes, there will be no strong interference to the MUE, and the MUE can normally measure an original serving cell (i.e., a cell of the macro base station) and maintain a normal connection with the original serving cell.
Referring to FIG. 3, the ABS subframes used by the UE in the coverage area of the femto base station are configured in the following scheme: three ABS subframes are configured for the femto base station, and the positions of these ABS subframes are coordinated at the network side and then notified to the UE, and after the non-member UE falls into the coverage area of the femto base station, the UE is scheduled by the macro base station and measures only in the ABS subframes, and the femto base station transmits only CRS signals in these ABS subframes, thereby effectively avoiding strong interference from the femto base station; and as illustrated in FIG. 3, there is further defined therein configuration modes of ABS subframes used by the UE in a coverage area of the pico base station and in measurement of the pico base station in a coverage area of the macro base station close to the pico base station, and since the UE can access the pico base station and there may be strong interference of the macro base station to the pico base station, the interference problem can be addressed by subframe obviation in the ABS subframes specified on the macro base station as illustrated in FIG. 3 whenever the UE suffers from interference of the macro base station either in the coverage area of the pico base station or in the coverage area of the macro base station.
In the prior art, due to deployment of various heterogeneous network nodes or due to network deployment for avoidance of a blind area, the UE may measure signals of a plurality of cells at the same site, for example, the UE accessing the pico base station detects signals of a plurality of macro base stations, and in another example, the UE accessing the macro base station detects signals of a plurality of femto base stations; and in order to lower the signaling size of ABS configuration signaling sent from the network side to the UE and enable the UE to measure signals of a plurality of cells with use of a common ABS configuration, ABS configurations of the plurality of cells can be required to be kept consistent (that is, kept in synchronization), and as specified in the existing protocol, ABS periodicity configurations between different base stations are transported over an interface connection: and in an FDD system, there is an ABS periodicity configuration of 40 ms, and in a TDD system, ABS periodicity configurations can be set to 20 ms/60 ms/70 ms dependent upon different TDD configurations.
In the existing LTE and LTE-A system, as specified in the protocol, control information carried on PDCCHs (Physical Downlink Control Channels) can only be transmitted in first several OFDM (Orthogonal Frequency Division Multiplexing) symbols of a subframe, and the UE can obtain common information and scheduling information thereof by blind detection among the PDCCH resources, and typically such PDCCH resources are referred to as “legacy PDCCH resources”, and an area where they are located is referred to as a “legacy PDCCH area”. Along with an increasing demand for scheduling signaling in CA (Carrier Aggregation), CoMP (Coordinated Multi-Point) transmission, enhanced Inter-Cell Interference Coordination (eICIC) and other services, the transmission capacity of the legacy PDCCH area has been becoming saturated, and consequently the PDCCHs need to be enhanced somehow.
An R-PDCCH currently supported in a relayed system is one of PDCCH enhancement solutions. Referring to FIG. 4, taking a carrier in a subframe as an example, in the relayed system, PDCCH resources and PDSCH (Physical Downlink Shared Channel) resources are structured as illustrated in FIG. 4, where an R-PDCCH is configured for the base station to transmit control signaling to the relay, and an R-PDSCH is configured for the relay to transmit data to the UE, and in order to enhance the capacity of PDCCHs in a non-relayed system, the PDCCH enhancement solution in the relayed system can also be introduced to the non-relayed system, that is, the base station spare a part of the PDSCH resources for transmission of data to be used for transmission of control signaling to the UE, and typically such PDCCH resources are referred to as “enhanced PDCCH resources”, and an area where they are located is referred to as an enhanced PDCCH area, which is an area of resources for transmission of data.
At present, the legacy PDCCH resources available to an interfering base station and a victim base station have been lowered for interference obviation due to the use of the TDM ICIC mechanism, and this may result in the problem of a limited capacity of the system, and consequently a specific search space has to be extended by the enhanced PDCCHs to thereby ensure the capacity of the system. With the use of the enhanced PDCCH solution, with the TDM ICIC mechanism either supported (that is, ABS subframes are configured at the interfering base station) or not supported, the UE accessing either the interfering base station or the victim base station will detect blindly in PDCCH common and user spaces in the legacy control area and the enhanced control area and demodulate common and specific control information carried on PDCCH without distinguishing between subframes, and this may result in unnecessary power consumption of or unnecessary interference to the UE. Specifically, after the interfering base station is configured with ABS subframes, the UE accessing the interfering base station may only be notified of a measurement limited set (this set is not equivalent to the actually configured set of ABS subframes), and even if the interfering base station does not transmit any control information in the ABS subframes so as to avoid interference, the UE accessing the interfering base station may search common spaces and specific spaces for a legacy PDCCH resource and an enhanced PDCCH resource of all the subframes after being notified of the measurement limited set, and alike an edge UE accessing the victim base station may also detect blindly in common spaces and specific spaces for a legacy PDCCH resource and an enhanced PDCCH resource of all the subframes, and this may result in unnecessary power consumption of the base station and the UE as well as unnecessary interference.
On the other hand, for uplink transmission of data, the base station needs to transmit an ACK/NACK feedback in the downlink, which is carried over a PHICH (Physical Hybrid-ARQ (Automatic Repeat reQuest) Indicator CHannel). For the FDD system, there are both uplink and downlink subframes, there is a PHICH resource in each subframe, and there is a relatively fixed timing relationship of the downlink ACK/NACK feedback with corresponding uplink data. For example, for uplink data transmitted in the n-th subframe, its corresponding ACK/NACK feedback is transmitted in the (n+4)-th downlink subframe. For the TDD system, there are a different number of uplink and downlink subframes in a different TDD subframe configuration, so ACK/NACK feedbacks of a plurality of uplink subframes may possibly be transmitted in the same downlink subframe. For example, for uplink data transmitted in the n-th subframe, its corresponding ACK/NACK feedback is transmitted in the (n+k)-th downlink subframe, where the value of k is set particularly as depicted in Table 1 below. For example, with the TDD uplink and downlink subframe configuration 0, uplink data transmitted in the second subframe has its corresponding ACK/NACK feedback transmitted in the sixth downlink subframe.
TABLE 1TDD uplinkanddownlinksubframeUplink subframe numberconfiguration0123456789047647614646266366646656646647
Referring to Table 1 below, with the TDD uplink and downlink subframe configuration 0, if the downlink subframe is configured as an ABS subframe at the interfering base station, then PHICH resources of the uplink subframes 3 and 4 transmitted from the victim base station can be avoided from interference of the interfering base station and thus protected when being transmitted in the downlink subframe 0, but control information carried on PHICH resources of the uplink subframes 3 and 4 transmitted from the interfering base station can not be scheduled because the downlink subframe 0 is configured as an ABS subframe for protection of the victim base station, and this may result in limited uplink transmission of the interfering base station: and in order to avoid this situation from occurring, an enhanced scheduling scheme can be considered for use, for example, multi-frame or cross-subframe scheduling in the uplink, but with the use of the enhanced scheduling scheme, the ABS subframe configuration condition may be unknowable so that PHICH transmission by the interfering base station may not be ensured. Alike for an accessing edge subscriber at the victim base station, uplink transmission may also be limited due to interference, and if an enhanced scheduling scheme is used, for example, multi-frame or cross-subframe scheduling in the uplink, then the ABS subframe configuration condition may be unknowable so that PHICH transmission by the victim base station may not be ensured.